Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art, and typically involve the use of a balloon catheter with a guidewire, possibly in combination with other intravascular devices such as stents. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold assembly attached to the proximal end. In use, the balloon catheter is advanced over the guidewire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated, and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures including fixed-wire (FW) catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art. An example of an OTW catheter may be found in commonly assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly assigned U.S. Pat. No. 5,156,594 to Keith.
The pushability and the trackability of a catheter are two performance characteristics essential to the success of intravascular catheters in medical procedures. Pushability refers to the catheter's ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the catheter's ability to navigate the tortuous vasculature of a patient. The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter. The distal portion is the section of the catheter that must track the guidewire through the small tortuous vessels of a patient's vasculature. The size of the distal tip, the flexibility of the distal tip and the lumen diameter all influence the trackability of a catheter. Imparting more flexibility to the distal portion of a catheter, in particular, is found to improve catheter trackability. Moreover, increasing the flexibility within the distal tip improves handling and navigation over a guidewire.
Materials particularly suitable for enhancing the pushability of a catheter also decrease a catheter's trackability, and the converse. For example, if a catheter is comprised entirely of a flexible polymeric material, the catheter loses pushability and may be unable to drive the balloon to its proper position within a patient's vasculature. Likewise, if a catheter is comprised entirely of a rigid polymeric material, the catheter may be unable to navigate the tortuous pathways of a patient's vasculature. As a result, prior art catheter manufacturers have reached compromises in materials and construction in order to accommodate these two conflicting performance characteristics.
In efforts to accentuate both pushability and trackability within a single catheter design, manufacturers have experimented with various catheter materials. A specific example of such material selection is the use of hypotube tubing. The term “hypotube,” as used herein, refers generally to a thin-walled, high-strength metallic tube having a lumen extending the length therein. The hypotube is preferably a stainless steel hypodermic tube that exhibits superior pushability characteristics.
Additionally, manufacturers have incorporated these various materials at particular locations on a catheter. Strategically positioning these materials along the length of a catheter frees manufacturers from the performance compromises associated with prior art catheters. For example, often the hypotube construction is incorporated within the proximal shaft region of a catheter, either entirely or in part, due to its superior pushability characteristics. Alternatively, a flexible polymeric material, such as high-density polyethylene, is incorporated within the distal shaft region of the same catheter.
An example of a catheter incorporating the enhanced pushability performance associated with a hypotube with the improved trackability of a flexible distal region is disclosed in U.S. Pat. No. 5,567,203,to Euteneuer, et al., the disclosure of which is incorporated herein by reference. In some embodiments, the Euteneuer et al. patent discloses an intravascular balloon catheter having a proximal hypotube shaft segment, a distal polymer shaft segment, a distally-mounted inflatable balloon segment, and a hollow tubular member having a proximal end connected to the distal end of the hypotube shaft segment such that the lumen of the hollow tubular member is in communication with the exterior of the balloon catheter, and the distal end of the hollow tubular member is connected to the distal end of the balloon.
The above-described materials that, in combination, accentuate medical device performance also tend to adhere poorly to one another. Bonds formed between these dissimilar materials are often exposed to stresses. Improvement in the bond between metal and polymeric components of a catheter shaft is desirable.